The disclosure of Japanese Patent Application No.2002-215391 filed on Jul. 24, 2002, including the specification, drawings and abstract are incorporated herein by reference in its entirety.
1. Field of Invention
The invention relates to an evaporated fuel processing apparatus for an internal combustion engine, and more particularly to an evaporated fuel processing apparatus suitable for effectively prevent the evaporated fuel generated in a fuel tank from being released to atmosphere.
2. Description of Related Art
There is disclosed an apparatus for processing evaporated fuel or fuel vapor generated within a fuel tank using a canister that adsorbs the fuel vapor so as not to be released to atmosphere, for example, in JP-A-6-93932. In such a generally employed fuel vapor processing apparatus, the intake negative pressure is introduced into the canister during operation of the internal combustion engine such that the fuel adsorbed in the canister is purged with air into an intake passage. This makes it possible to restore the fuel adsorbing capability of the canister without releasing the fuel into atmosphere during operation of the internal combustion engine.
In the aforementioned fuel vapor processing apparatus, quantity of injected fuel is adjusted so as to offset the quantity for purging. This allows the fuel in the canister to be purged into the internal combustion engine without varying the air/fuel ratio of the internal combustion engine.
In order to correct the fuel injection quantity accurately upon purging of the fuel in the canister into the intake passage, it is necessary to accurately detect the quantity of the fuel supplied through purging. Accordingly it is preferable to detect the fuel adsorbing state in the canister appropriately so as to accurately detect the quantity of the fuel supplied through purging.
The aforementioned apparatus is structured to monitor the temperature inside the canister and the temperature change is time integrated, based on which the fuel adsorbing state of the canister is estimated. Adsorption of the fuel vapor in the canister may cause an exothermic reaction. On the contrary, desorption of the fuel from the canister may cause an endothermic reaction. The temperature inside the canister, therefore, varies as the fuel is adsorbed in or released from the canister. The time integral value of the inner temperature is correlated with the residual state of the fuel in the canister. In the aforementioned apparatus, the fuel adsorbing state in the canister can be estimated with accuracy to a certain degree.
The change in the temperature inside the canister depends on the increase or decrease in the fuel adsorbed in the canister. The time integration of the temperature change may be effective for detecting the relative change in the quantity of the fuel in the canister. The absolute quantity of the fuel adsorbed in the canister, however, cannot be obtained by the aforementioned apparatus.
It is necessary to detect the absolute quantity of the fuel adsorbed in the canister for accurately detecting the quantity of the fuel supplied through purging. The detection of the fuel adsorbing state of the canister performed in the aforementioned apparatus, thus, is not sufficient to allow accurate correction of the fuel injection quantity.
It is an object of the invention to provide an evaporated fuel processing apparatus capable of detecting an absolute quantity of the fuel adsorbed in the canister accurately.
According to an embodiment of the invention, an evaporated fuel processing apparatus for an internal combustion engine includes a canister that adsorbs a fuel vapor generated within a fuel tank, a gas flow detecting mechanism that detects a flow of gas at least at a predetermined flow rate between the fuel tank and the canister. The predetermined flow rate is higher than a flow rate of gas normally flowing between the fuel tank and the canister which are communicated with each other. The apparatus further includes a canister temperature detector that detects a temperature of the canister, and a controller that detects one of an upper peak value and a lower peak value of the temperature of the canister caused in a continual state of the flow of gas at least at the predetermined flow rate detected by the gas flow detecting mechanism, and estimates a fuel adsorbing state within the canister on the basis of the canister temperature obtained subsequent to a detection of the one of the upper peak value and the lower peak value. According to an embodiment of the invention, the peak value of the canister temperature is detected in the condition where a large quantity of gas flows between the fuel tank and the canister. In the case where the fuel is adsorbed, the canister temperature reaches the peak temperature at a time when the canister no longer adsorbs the fuel. Meanwhile in the case where the fuel is desorbed, the canister temperature reaches the peak temperature at a time when the canister no longer desorbs the fuel. In the aforementioned cases, the absolute quantity of the fuel adsorbed in the canister is determined in accordance with the canister temperature, that is, the canister peak temperature. Accordingly, the fuel adsorbing state corresponding to the absolute quantity of the adsorbed fuel may be accurately estimated on the basis of the canister temperature subsequent to the peak temperature.
In the embodiment, the canister includes a purge port communicated with an intake passage of the internal combustion engine, and the canister temperature detector comprises a canister temperature sensor disposed around the purge port such that a temperature within the canister is detected. According to the embodiment, the canister temperature is detected around the purge port of the canister. The fuel adsorbing state around the purge port can be particularly detected with high accuracy. After the start of purging of the fuel, the fuel vapor concentration of the gas to be first purged is greatly influenced by the fuel adsorbing state of the canister around the purge port. If the fuel adsorbing state around the purge port can be accurately detected, the fuel vapor concentration of the purge gas may be accurately estimated immediately after the start of purging. This makes it possible to generate a large quantity of fuel to be purged.
In the embodiment, the controller obtains a fuel vapor concentration of the gas flowing between the fuel tank and the canister in the continual state of the flow of gas at least at the predetermined flow rate, and a flow rate of the gas flowing between the fuel tank and the canister in the continual state of the flow of gas at least at the predetermined flow rate. The controller further estimates the fuel adsorbing state on the basis of the canister temperature obtained subsequent to the detection of the one of the upper peak value and the lower peak value, the fuel vapor concentration, and the flow rate of the gas. According to the embodiment, the fuel adsorbing state can be estimated on the basis of the fuel vapor concentration of the gas that flows between the fuel tank and the canister, and the flow rate of the gas in addition to the canister temperature after reaching the peak temperature. This makes it possible to accurately estimate the fuel adsorbing state of the canister.
In the embodiment, the controller contains a map that stores the fuel adsorbing state within the canister defined by the canister temperature, the fuel vapor concentration, and the flow rate of the gas. The controller refers to the map so as to determine the fuel adsorbing state in accordance with the canister temperature obtained subsequent to the detection of the one of the upper peak value and the lower peak value, the fuel vapor concentration, and the flow rate of the gas. According to the embodiment, the fuel adsorbing state of the canister can be simply and yet accurately estimated by referring to the map of the fuel adsorbing state of the canister, which is defined by the canister temperature, fuel vapor concentration, and the flow rate of the gas.
In the embodiment, the gas flow detecting mechanism detects a flow of gas containing fuel vapor at least at the predetermined flow rate from the fuel tank to the canister upon a fuel supply. According to the embodiment, the fuel adsorbing state of the canister may be accurately estimated on the basis of the flow of a large quantity of the gas containing the fuel vapor in the direction from the fuel tank to the canister during the fuel supply.
In the embodiment, a tank vapor temperature detector that detects a vapor temperature within the fuel tank is provided. The controller obtains a saturated vapor pressure of a fuel vapor within the fuel tank on the basis of the vapor temperature, and further obtains a concentration of the fuel vapor on the basis of a ratio of the saturated vapor pressure to an atmospheric pressure. According to the embodiment, the fuel vapor concentration is obtained in the condition where the pressure within the fuel tank is held substantially equal to the atmospheric pressure during the fuel supply. In this case, the saturated vapor pressure of the fuel vapor is calculated on the basis of the vapor temperature. The fuel vapor concentration is accurately obtained on the basis of the saturated vapor pressure and the ratio of the saturated vapor pressure to the atmospheric pressure.
In the embodiment, a space capacity detector that detects a space capacity of the fuel tank is provided. The controller obtains a flow rate of the gas on the basis of a change in the space capacity detected by the space capacity detector as an elapse of time. According to the embodiment, the flow rate of the gas is obtained in the condition where the fluid level of the fuel tank rises as the supply of the fuel, and the space capacity of the fuel tank is accordingly decreased as time elapses from the fuel supply. In this case, the flow rate of the gas is calculated on the basis of the change in the space capacity as the elapse of time.
In an another embodiment of the invention, an in-tank control valve that controls communication between the fuel tank and the canister, and a differential pressure detector that detects a differential pressure generated between a side of the fuel tank and a side of the canister with respect to the in-tank control valve in a closed state are provided. The controller serves to open the in-tank control valve when the detected differential pressure is at least a predetermined valve opening pressure such that the gas flows at least at the predetermined flow rate between the fuel tank and the canister. According to the embodiment, when the differential pressure is generated between the fuel tank side and the canister side with respect to the in-tank pressure control valve, such in-tank pressure control valve is opened so as to allow a large quantity of the gas to flow between the fuel tank and the canister. In this case, the fuel adsorbing state of the canister may be estimated by causing a large quantity of the gas to flow.
In the embodiment, a tank vapor temperature detector that detects a vapor temperature within the fuel tank is provided. The controller obtains a saturated vapor pressure of a fuel vapor within the fuel tank on the basis of the tank vapor temperature, an inner pressure of the fuel tank, and a first fuel vapor concentration on the basis of a ratio of the saturated vapor pressure to the inner pressure of the fuel tank when the gas flows at least at the predetermined flow rate from the fuel tank to the canister. According to the embodiment, the saturated vapor pressure of the fuel vapor is calculated in the case where a large quantity of the gas flows from the fuel tank to the canister as the in-tank pressure control valve is opened. The fuel vapor concentration is accurately calculated on the basis of the ratio of the saturated vapor pressure to the in-tank pressure.
In the embodiment, the controller obtains a saturated vapor pressure of the fuel vapor within the canister on the basis of the canister temperature, and a second fuel vapor concentration on the basis of a ratio of the saturated vapor pressure to an atmospheric pressure when the gas flows at least at the predetermined flow rate from the canister to the fuel tank. According to the embodiment, the saturated vapor pressure of the fuel vapor in the canister is calculated on the basis of the canister temperature in the case where a large quantity of the gas flows from the canister to the fuel tank as the in-tank pressure control valve is opened. The fuel vapor concentration is accurately calculated on the basis of the ratio of the saturated vapor pressure to the atmospheric pressure.
In the embodiment, the controller obtains the inner pressure of the fuel tank, and a first flow rate of the gas that flows at least at the predetermined flow rate from the fuel tank to the canister using a formula: Formula:   m  =      Cd    ⁢          xe2x80x83        ⁢          Pin              RTin              ⁢    Aval    ⁢          xe2x80x83        ⁢                  (                  Pout          Pin                )                    1        r              ⁢                                        2            ⁢            r                                r            -            1                          ⁢                  {                      1            -                                          (                                  Pout                  Pin                                )                                                              r                  -                  1                                r                                              }                    
where Pout as a pressure at an outflow side represents the inner pressure of the fuel tank, Tin as a temperature at an inflow side represents the canister temperature, Pin as a pressure at the inflow side represents the atmospheric pressure, Cd represents a flow rate coefficient indicating compressibility, r represents a ratio of the specific heat, R represents a gas constant, and Aval represents an opening area of the in-tank control valve. According to the embodiment, the flow rate m of a large quantity of the gas flowing from the fuel tank to the canister is obtained by substituting the vapor temperature in the fuel tank as the outflow temperature Tout, the inner pressure of the fuel tank as the outflow pressure Pout, the canister temperature as the inflow temperature Tin, and the atmospheric pressure as the inflow pressure Pin in a predetermined formula.
In the embodiment, the controller obtains the tank vapor temperature within the fuel tank, the inner pressure of the fuel tank, and a second flow rate of the gas that flows at least at the predetermined flow rate from the canister to the fuel tank using a formula: Formula:   m  =      Cd    ⁢          xe2x80x83        ⁢          Pin              RTin              ⁢    Aval    ⁢          xe2x80x83        ⁢                  (                  Pout          Pin                )                    1        r              ⁢                                        2            ⁢            r                                r            -            1                          ⁢                  {                      1            -                                          (                                  Pout                  Pin                                )                                                              r                  -                  1                                r                                              }                    
where Pout as the pressure at the outflow side represents the atmospheric pressure, the Tin as the temperature at the inflow side represents the tank vapor temperature within the fuel tank, the Pin as the pressure at the inflow side represents the inner pressure of the fuel tank, Cd represents the flow rate coefficient indicating compressibility, r represents the ratio of the specific heat, R represents the gas constant, and Aval represents the opening area of the in-tank control valve. According to the embodiment, the flow rate m of a large quantity of the gas flowing from the canister to the fuel tank is obtained by substituting the canister temperature as the outflow temperature Tout, the atmospheric pressure as the outflow pressure Pout, the vapor temperature within the fuel tank as the inflow temperature Tin, and the inner pressure of the fuel tank as the inflow pressure Pin in a predetermined formula.
In the embodiment, the controller includes an in-tank pressure sensor for detecting the inner pressure of the fuel tank. According to the embodiment, the inner pressure of the fuel tank can be easily detected by the in-tank pressure sensor.
In another embodiment, a space capacity detector that detects a space capacity of the fuel tank is provided. The controller obtains the saturated vapor pressure of the fuel vapor within the fuel tank on the basis of the tank vapor temperature, and serves to block the fuel tank by closing the in-tank pressure control valve after the inner pressure of the fuel tank becomes the atmospheric pressure. The controller further obtains a total number of moles of the gas within the fuel tank on the basis of the space capacity, the vapor temperature, and the atmospheric pressure obtained when the fuel tank is blocked; a number of moles of air within the fuel tank on the basis of a ratio of the saturated vapor pressure to the atmospheric pressure and the total number of moles; a partial pressure of air within the fuel tank on the basis of the number of moles of air, the space capacity, and the vapor temperature obtained when a block state of the fuel tank is held; and an inner pressure of the fuel tank by adding the saturated vapor pressure to the partial pressure of air. According to the embodiment, the number of moles of air within the fuel tank can be calculated on the basis of the total number of moles of the gas within the fuel tank, the saturated vapor pressure of the fuel, the in-tank pressure (atmospheric pressure) at a time when the fuel tank is disconnected from the canister. Subsequently, the air partial pressure within the fuel tank may be obtained on the basis of the number of moles, and the space capacity and the vapor temperature at the respective time points. The inner pressure of the fuel tank may be obtained by adding the calculated air partial pressure to the saturated vapor pressure at that time.